1. IntroductionTheTheaetetus,which probably dates from about 369 BC, is arguably Plato's greatest work on epistemology. (Arguably, it is his greatest work on anything.) Plato (c.427347 BC) has much to say about the nature of knowledge elsewhere. But only theTheaetetusoffers a set-piece discussion of the question What is knowledge?Like many other Platonic dialogues, theTheaetetusis dominated by question-and-answer exchanges, with Socrates as main questioner. His two respondents are Theaetetus, a brilliant young mathematician, and Theaetetus' tutor Theodorus, who is rather less young (and rather less brilliant).Also like other Platonic dialogues, the main discussion of theTheaetetusis set within a framing conversation (142a-143c) between Eucleides and Terpsion (cp.Phaedo59c). This frame may be meant as a dedication of the work to the memory of the man Theaetetus. Sedley 2004 (68) has argued that it is meant to set some distance between Plato's authorial voice and the various other voices (including Socrates') that are heard in the dialogue. Alternatively, or also, it may be intended, likeSymposium1723, to prompt questions about the reliability of knowledge based on testimony. (Cp. the law-court passage (Theaetetus201a-c), and Socrates' dream (Theaetetus201c-202c).)TheTheaetetus most important similarity to other Platonic dialogues is that it isaporeticit is a dialogue that ends in animpasse. TheTheaetetusreviews three definitions of knowledge in turn; plus, in a preliminary discussion, one would-be definition which, it is said, does not really count. Each of these proposals is rejected, and no alternative is explicitly offered. Thus we complete the dialogue without discovering what knowledge is. We discover only three things that knowledge isnot(Theaetetus210c; cp. 183a5, 187a1).This matters, given the place that theTheaetetusis normally assigned in the chronology of Plato's writings. Most scholars agree that Plato's first writings were the Socratic dialogues (as they are often called), which ask questions of the What is? form and typically fail to find answers: What is courage? (Laches), What is self-control? (Charmides), What is justice? (Alcibiades I;Republic1), What is holiness? (Euthyphro), What is friendship? (Lysis), What is virtue? (Meno), What is nobility? (Hippias Major). After some transitional works (Protagoras, Gorgias, Cratylus, Euthydemus) comes a series of dialogues in which Plato writes to a less tightly-defined format, not always focusing on a What is? question, nor using the question-and-answer interrogative method that he himself depicts as strictly Socratic: thePhaedo, thePhaedrus, theSymposium,and theRepublic. In these dialogues Plato shows a much greater willingness to put positive and ambitious metaphysical views in Socrates' mouth, and to make Socrates the spokesman for what we call Plato's theory of Forms.After these, it is normally supposed that Plato's next two works were theParmenidesand theTheaetetus, probably in that order. If so, and if we take as seriously as Plato seems to the important criticisms of the theory of Forms that are made in theParmenides, then the significance of theTheaetetus's return to the aporetic method looks obvious. Apparently Plato has abandoned the certainties of his middle-period works, such as the theory of Forms, and returned to the almost-sceptical manner of the early dialogues. In theTheaetetus, the Forms that so dominated theRepublic's discussions of epistemology are hardly mentioned at all. A good understanding of the dialogue must make sense of this fact.2. Summary of the DialogueAt the gates of the city of Megara in 369 BC, Eucleides and Terpsion hear a slave read out Eucleides' memoir of a philosophical discussion that took place in 399 BC, shortly before Socrates' trial and execution (142a-143c). In this, the young Theaetetus is introduced to Socrates by his mathematics tutor, Theodorus. Socrates questions Theaetetus about the nature of expertise, and this leads him to pose the key question of the dialogue: What is knowledge? (143d-145e). Theaetetus' first response (D0) is to give examples of knowledge such as geometry, astronomy, harmony, arithmetic (146a-c). Socrates objects that, for anyx, examples ofxare neither necessary nor sufficient for a definition ofx(146d-147e). Theaetetus admits this, and contrasts the ease with which he and his classmates define mathematical terms with his inability to define of knowledge (147c-148e). Socrates offers to explain Theaetetus' bewilderment about the question What is knowledge? by comparing himself with a midwife: Theaetetus, he suggests, is in discomfort because he is in intellectual labour (148e-151d).Thus prompted, Theaetetus states his first acceptable definition, which is the proposal (D1) that Knowledge is perception (151d-e). Socrates does not respond to this directly. Instead he claims that D1 entails two other theories (Protagoras' and Heracleitus'), which he expounds (151e-160e) and then criticises (160e-183c). Socrates eventually presents no fewer than eleven arguments, not all of which seem seriously intended, against the Protagorean and Heracleitean views. If any of these arguments hit its target, then bymodus tollensD1 is also false. A more direct argument against D1 is eventually given at 1847.In 187b48, Theaetetus proposes a second definition of knowledge: (D2) Knowledge is true belief. D2 provokes Socrates to ask: how can there be any such thing asfalsebelief? There follows a five-phase discussion which attempts to come up with an account of false belief. All five of these attempts fail, and that appears to be the end of the topic of false belief. Finally, at 200d-201c, Socrates returns to D2 itself. He dismisses D2 just by arguing that accidental true beliefs cannot be calledknowledge, giving Athenian jurymen as an example of accidental true belief.Theaetetus tries a third time. His final proposal (D3) defines knowledge astrue belief with an account (logos) (201c-d). The ensuing discussion attempts to spell out what it might be like for D3 to be true, then makes three attempts to spell out what alogosis.In 201d-202d, the famous passage known asThe Dream of Socrates, a two-part ontology of elements and complexes is proposed. Parallel to this ontology runs a theory of explanation that claims that to explain, to offer alogos,is to analyse complexes into their elements, i.e., those parts which cannot be further analysed. Crucially, the Dream Theory says that knowledge ofOis true belief aboutOplus an account ofO's composition. IfOis not composite,Ocannot be known, but only perceived (202b6). When Socrates argues against the Dream Theory (202d8206b11), it is this entailment that he focuses on.Socrates then turns to consider, and reject, three attempts to spell out what alogosisto give an account of account. The first attempt takeslogosjust to mean speech or statement (206c-e). The second account (206e4208b12) of logosofO takes it as enumeration of the elements ofO. The third and last proposal (208c1210a9) is that to give thelogosofOis to cite thesmeionordiaphoraofO, the sign or diagnostic feature whereinOdiffers from everything else.All three attempts to give an account of account fail. The day's discussion, and the dialogue, end inaporia.Socrates leaves to face his enemies in the courtroom.3. Overall Interpretations of theTheaetetusTheTheaetetusis a principal field of battle for one of the main disputes between Plato's interpreters. This is the dispute betweenUnitariansandRevisionists.Unitarians argue that Plato's works display a unity of doctrine and a continuity of purpose throughout. Unitarians include Aristotle, Proclus, and all the ancient and mediaeval commentators; Bishop Berkeley; and in the modern era, Schleiermacher, Ast, Shorey, Dis, Ross, Cornford, and Cherniss.Revisionists retort that Plato's works are full of revisions, retractations, and changes of direction. Eminent Revisionists include Lutoslawski, Ryle, Robinson, Runciman, Owen, McDowell, Bostock, and many recent commentators.Unitarianism is historically the dominant interpretive tradition. Revisionism, it appears, was not invented until the text-critical methods, such as stylometry, that were developed in early nineteenth-century German biblical studies were transferred to Plato.In the twentieth century, a different brand of Revisionism has dominated English-speaking Platonic studies. This owes its impetus to a desire to read Plato as charitably as possible, and a belief that a charitable reading of Plato's works will minimise their dependence on the theory of Forms. (Corollary: Unitarians are likelier than Revisionists to be sympathetic to the theory of Forms.)Unitarianismcouldbe the thesis that all of Plato's work is, really, Socratic in method and inspiration, and that Plato should be credited with no view that is not endorsed in the early dialogues. (In some recent writers, Unitarianismisthis thesis: see Penner and Rowe (2005).) But this is not the most usual form of Unitarianism, which is more likely to read back the concerns of thePhaedoand theRepublicinto the Socratic dialogues, than to read forward the studied agnosticism of the early works into these more ambitious later dialogues. Likewise, Revisionismcouldbe evidenced by the obvious changes of outlook that occur, e.g., between theCharmidesand thePhaedo, or again between theProtagorasand theGorgias. But the main focus of the Revisionist/Unitarian debate has never been on these dialogues. The contrasts between theCharmidesand thePhaedo, and theProtagorasand theGorgias,tell us little about the question whether Plato ever abandoned the theory of Forms. And that has usually been the key dispute between Revisionists and Unitarians.Hence the debate has typically focused on the contrast between the the Middle Period dialogues and the Late dialogues. Revisionists say that the Middle Period dialogues enounce positive doctrines, above all the theory of Forms, which the Late dialogues criticise, reject, or simply bypass. The main place where Revisionists (e.g., Ryle 1939) suppose that Plato criticises the theory of Forms is in theParmenides(though some Revisionists find criticism of the theory of Forms in theTheaetetusandSophistas well). The main places where Revisionists look to see Plato managing without the theory of Forms are theTheaetetusandSophist.Ryle's Revisionism was soon supported by other Oxford Plato scholars such as Robinson 1950 and Runciman 1962 (28). Revisionism was also defended by G.E.L. Owen. More recently, McDowell 1976, Bostock 1988, and Burnyeat 1990 are three classic books on theTheaetetusof a decidedly Revisionist tendency. (McDowell shows a particularly marked reluctance to bring in the theory of Forms anywhere where he is not absolutely compelled to.)Revisionists are committed by their overall stance to a number of more particular views.They are more or less bound to say that the late Plato takes theParmenides'critique of the theory of Forms to be cogent, or at least impressive; that theSophists theory of the five greatest kinds (Sophist254b-258e) is not a development of the theory of Forms; and that theTimaeuswas written before theParmenides,because of theTimaeus'apparent defence of theses from the theory of Forms. Their line on theTheaetetuswill be that its argument does not support the theory of Forms; that theTheaetetusis interesting precisely because it shows us how good at epistemology Plato is once hefreeshimself from his obsession with the Forms.Some of these Revisionist claims look easier for Unitarians to dispute than others. For example, Plato does not think that the arguments ofParmenides130b-135c actuallydisprovethe theory of Forms. Rather, it is obviously Plato's view that Parmenides' arguments against the Forms can be refuted. SeeParmenides135a-d, where Plato explicitly saysusing Parmenides as his mouthpiecethat these argumentswillbe refuted by anyone of adequate philosophical training. (Whether anyone of adequate philosophical training is available is, of course, another question.)Another problem for the Revisionist concerns Owen 1965's proposal, adopted by Bostock 1988, to redate theTimaeusto the Middle Period, thus escaping the conclusion that Plato still accepted the theory of Forms at the end of his philosophical career. The trouble with this is that it is not only theTimaeusthat the Revisionist needs to redate. In quite a number of apparently Late dialogues, Plato seems sympathetic to the theory of Forms: see e.g.,Philebus61e andLaws965c.On the other hand, the Revisionist claim that theTheaetetusshows Plato doing more or less completely without the theory of Forms is very plausible. There are no explicit mentions of the Forms at all in theTheaetetus, except possibly (and even this much is disputed) in what many take to be the philosophical backwater of the Digression. The main argument of the dialogue seems to get along without even implicit appeal to the theory of Forms. In theTheaetetus, Revisionism seems to be on its strongest ground of all.The usual Unitarian answer is that this silence is studied. In theTheaetetus,Unitarians suggest, Plato is showing what knowledgeis not. His argument is designed to show that certain sorts of alternatives to Plato's own account of knowledge must fail. Plato demonstrates this failure by the maieutic method of developing those accountsuntilthey fail. Thus theTheaetetusshows the impossibility of a successful account of knowledge that does not invoke the Forms.The fault-line between Unitarians and Revisionists is the deepest fissure separating interpreters of theTheaetetus. It is not the only distinction among overall interpretations of the dialogue. It has also been suggested, both in the ancient and the modern eras, that theTheaetetusis a sceptical work; that theTheaetetusis a genuinely aporetic work; and that theTheaetetusis a disjointed work. However, there is no space to review these possibilities here. It is time to look more closely at the detail of the arguments that Plato gives in the distinct sections of the dialogue.4. The Introduction to the Dialogue: 142a-145eWe should not miss the three philosophical theses that are explicitly advanced in the Introduction. They are offered without argument by Socrates, and agreed to without argument by Theaetetus, at 145d7145e5:1. The wise are wisesophiai(= by/ because of/ in respect of/ as a result of wisdom:145d11).2. To learn is to become wiser about the topic you are learning about (145d89).3. Wisdom (sophia) and knowledge (epistm) are the same thing (145e5).All three theses might seem contentious today. (1) seems to allude toPhaedo100e's notorious thesis about the role of the Form ofF-ness in anyx's beingFthatxisFbythe Form ofF-ness. (2) looks contentious because it implies (3); and (3) brings me to a second question about 142a-145e (which is also an important question about the whole dialogue): What is the meaning of the Greek word that I am translating as knowledge,epistm?Much has been written about Plato's words for knowledge. One important question raised by Runciman 1962 is the question whether Plato was aware of the commonplace modern distinction between knowing that, knowing how, and knowing what (or whom). Nothing is more natural for modern philosophers than to contrast knowledge of objects (knowledge by acquaintance or objectual knowledge; Frenchconnatre) with knowledge of how to do things (technique knowledge), and with knowledge of propositions or facts (propositional knowledge; Frenchsavoir). Runciman doubts that Plato is aware of this threefold distinction (1962, 17): At the time of writing theTheaetetusPlato had made no clear distinction [between] knowing that, knowing how, and knowing by acquaintance.Against this, Plato's word for knowing how is surelytekhn, from which we get the English word technique. Plato obviously thinkstekhnincidental to a serious discussion ofepistm. This is part of the point of the argument against definition by examples that begins at 146d (cp. 177c-179b).As for the difference between knowing that and knowledge by acquaintance: theTheaetetusdoes mix passages that discuss the one sort of knowledge with passages that discuss the other. This does not imply that Plato was unaware of the difference. Perhaps he wants to discuss theories of knowledge that find deep conceptual connections between the two sorts of knowledge.A grammatical point is relevant here. The objectual I knowSocratesin classical Greek isoida(orgignsk)ton Skratn; the propositional I know Socratesis wiseisoida(orgignsk)ton Skratnsophon einai, literally I know Socratesto bewise. The to be (einai) is idiomatically dispensable; dispensing with it, we getoida ton Skratnsophon, literally I know (the)wiseSocrates. Thus Greek idiom can readily treat the object of propositional knowledge, which in English would most naturally be a that-clause, as athing considered as having a quality. We might almost say that Greek treats what is known in propositional knowledge as just one special case of what is known in objectual knowledge. This suggests that the ancient Greeks naturally saw propositional and objectual knowledge as more closely related than we do (though not necessarily as indistinguishable). If so, Plato may have felt able to offer a single treatment for the two kinds of knowledge without thereby confusing them. The point will be relevant to the whole of theTheaetetus.5. Definition by Examples: 146a-151dAt 145d Socrates states the one little question that puzzles him: What is knowledge? Theaetetus' first response (D0) is to offer examples of knowledge (146c). Socrates rejects this response, arguing that, for anyx, examples ofxare neither necessary nor sufficient for a definition ofx. They are not necessary, because they are irrelevant (146e). They are not sufficient, because they presuppose the understanding that a definition is meant to provide (147a-b). Moreover (147c), a definition could be briefly stated, whereas talking about examples is an interminable diversion (aperanton hodon).Does Socrates produce good arguments against definition by examples? Many philosophers think not (McDowell 1976 (115), Geach 1966, Santas 1972, Burnyeat 1977). They often argue this by appealing to the authority of Wittgenstein, who famously complains (The Blue and Brown Books, 20) that When Socrates asks the question, What is knowledge?, he does not regard it even as apreliminaryanswer to enumerate cases of knowledge. For arguments against this modern consensus, see Chappell 2005 (3637).Some commentators have taken Socrates' critique of definition by examples to be an implicit critique of theRepublic's procedure of distinguishing knowledge, belief, and ignorance by distinguishing their objects. The suggestion was first made by Ryle 1990 (23), who points out that Socrates makes it clear that what he wants discussed is not a list of things that people know, but an elucidation of the concept of knowledge. Ryle suggests that Attention to this simple point might have saved Cornford from saying that the implicit conclusion of the dialogue is that true knowledge has for its objects things of a different order. Ryle thinks it silly to suggest that knowledge can be defined merely by specifying its objects.However, 145e-147c cannot be read as a critique of theRepublic's procedure of distinguishing knowledge from belief by their objects. 145e-147c is not against defining knowledge by examples ofobjectsof knowledge; it is against defining knowledge by examples ofkindsof knowledge. (See e.g., 146e7, We weren't wanting to make a list of kinds of knowledge.) This is a different matter.Why, anyway, would the Platonist of theRepublicthink that examples of the objects of knowledge are enough for a definition of knowledge? He is surely the last person to think that. The person whowillthink this is the empiricist, who thinks that we acquire all our concepts by exposure to examples of their application: Locke,EssayII.1, Aristotle,Posterior Analytics100a49. For the Platonist, definition by examples is never even possible; for the empiricist, definition by examples is the natural method in every case. This suggests that empiricism is a principal target of the argument of theTheaetetus. More about this in sections 68.Theaetetus is puzzled by his own inability to answer Socrates' request for a definition of knowledge, and contrasts it with the ease with which he can provide mathematical definitions. He gives an example of a mathematical definition; scholars are divided about the aptness of the parallel between this, and what would be needed for a definition of knowledge. Socrates' response, when Theaetetus still protests his inability to define knowledge, is to compare himself to a midwife in a long and intricate analogy.Many ancient Platonists read the midwife analogy, and more recently Cornford 1935 has read it, as alluding to the theory of recollection. But it is better not to import metaphysical assumptions into the text without good reason, and it is hard to see what the reason would be beyond a determination to insist that Plato always maintained the theory of recollection. With or without this speculation, the midwife passage does tell us something important about how theTheaetetusis going to proceed. In line with the classification that the ancient editors set at the front of the dialogue, it is going to bepeirastikos, anexperimentaldialogue. It will try out a number of suggestions about the nature of knowledge. As in the aporetic dialogues, there is no guarantee that any of these suggestions will be successful (and every chance that none of them will be).So read, the midwife passage can also tell us something important about the limitations of theTheaetetus'inquiry. The limitations of the inquiry are the limitations of the main inquirers, and neither (the historical) Socrates nor Theaetetus was a card-carrying adherent of Plato's theory of Forms. Perhaps the dialogue brings us only as far as the threshold of the theory of Forms precisely because, on Socratic principles, one can get no further. To get beyond where theTheaetetusleaves off, you have to be a Platonist. (For book-length developments of this reading of theTheaetetus,see Sedley 2004 and Chappell 2005.)6. First Definition (D1): Knowledge is Perception: 151e-187aBetween Stephanus pages 151 and 187, and leaving aside the Digression, 172177 (section 6d), 31 pages of close and complex argument state, discuss, and eventually refute the first of Theaetetus' three serious attempts at a definition of knowledge (D1): Knowledge is perception.As before, there are two main alternative readings of 151187: the Unitarian and the Revisionist. On the Unitarian reading, Plato's purpose is to salvage as much as possible of the theories of Protagoras and Heracleitus (each respectfully described asou phaulon: 151e8, 152d2). Plato's strategy is to show that these theories have their own distinctive area of application, the perceptible or sensible world, within which they are true. However, the sensible world is not the whole world, and so these theories are not the whole truth. We get absurdities if we try to take them as unrestrictedly true. To avoid these absurdities it is necessary to posit theintelligible world(the world of the Forms) alongside thesensible world(the world of perception). When this is done, Platonism subsumes the theories of Protagoras and Heracleitus as partial truths. On this reading, the strategy of the discussion of D1 is to transcend Protagoras and Heracleitus: to explain their views by showing how they are, not the truth, but parts of a larger truth. In the process the discussion reveals logical pressures that may push us towards the two-worlds Platonism that many readers, e.g., Ross and Cornford, find in theRepublicandTimaeus.On the Revisionist reading, Plato's purpose is to refute the theories of Protagoras and Heracleitus. He thinks that the absurdities those theories give rise to, come not from trying to take the theories asunrestrictedlytrue, but from trying to take them as trueat all, even of the sensible world. Anyone who tries to take seriously the thesis that knowledge is perception has to adopt theories of knowledge and perception like Protagoras' and Heracleitus'. But their theories are untenable. Bymodus tollensthis shows that D1 itself is untenable. On this reading, the strategy of the discussion of D1 is to move us towards the view that sensible phenomena have to fall under the same general metaphysical theory as intelligible phenomena.This outline of the two main alternatives for 151187 shows how strategic and tactical issues of Plato interpretation interlock. For instance, the outline shows how important it is for an overall understanding of theTheaetetusto have a view on the following questions of detail (more about them later):1. At 156a-157c, is Socrates just reporting, or also endorsing, a Heracleitean flux theory of perception?2. What is the date of theTimaeus, which seems (2829, 45b46c, 49e) to present a very similar theory of perception to that found inTheaetetus1567?3. What does Plato take to be the logical relations between the three positions under discussion in 151184 (D1, Protagoras' theory, and Heracleitus' theory)? The closer he takes them to be, the more support that seems to give to the Revisionist view that the whole of 151187 is one giganticmodus tollens. The more separate they are, the better for those versions of Unitarianism that suggest that Plato wants to pick and choose among the positions offered in 151187.So much for the overall structure of 151187; now for the parts.6.1 The Definition of Knowledge as Perception: 151d-eAt 151d7-e3 Theaetetus proposes D1: Knowledge isnothing other thanperception (aisthsis). This proposal is immediately equated by Socrates with Protagoras's thesis that man is the measure of all things (Hm forhomomensura), which in turn entails the thesis that things are to any human just as they appear to that human (PS for phenomenal subjectivism). Socrates then adds that, in its turn, PS entails Heracleitus' view that All is flux, that there are no stably existingobjectswith stably enduringqualities.The first of these deft exchanges struck the Anonymous Commentator as disingenuous: Plato himself knew that Protagoras' opinion about knowledge was not the same as Theaetetus' (Anon,ad loc.). Certainly it is easy to see counter-examples to the alleged entailment. Take, for instance, the thesis that knowledge isawareness(which is often the right way to translateaisthsis). Or take the thesis that to know is to perceive things as God, or the Ideal Observer, perceives them, and that we fail to know (or to perceive) just insofar as our opinions are other than God's or the Ideal Observer's. These theses are both versions of D1. Neither entails Hm, the claim that man is the measure of all things; nor the Protagoreanism that lies behind that slogan.So how, if at all, does D1 entail all the things that Socrates apparently makes it entail in 151184? And does Plato think it has all these entailments? Evidently the answer to that depends on how we understand D1. In particular, it depends on the meaning of the wordaisthsis, perception, in D1. If the slogan Knowledge is perception equates knowledge with what ordinary speakers of classical Greek would have meant byaisthsis, then D1 does not entail Protagoras' and Heracleitus' views. In the ordinary sense ofaisthsis, there are (as just pointed out) too many other possible ways of spelling out D1 for the move from D1 to Hm to be logically obligatory. But if the slogan Knowledge is perception equates knowledge with what Protagoras and Heracleitus meant byaisthsis, D1doesentail Protagoras' and Heracleitus' views. Of course it does; for then D1 simply says that knowledge is just what Protagoras and Heracleitus say knowledge is.6.2 The Cold Wind Argument; and the Theory of Flux: 152a-160eAt 152b1152c8 Socrates begins his presentation of Protagoras' view that things are to any human just as they appear to that human by taking the example of a wind which affects two people differently. Such cases, he says, support Protagoras' analysis: that the wind is coldto the one who feels cold, but not coldto the one who does not feel cold.Some scholars (Cornford 1935, 334; Waterlow 1977) think that the point of the argument is thatboththe wind in itself is cold and the wind in itself is not cold (but warm) are true: Warm and cold are two properties which can co-exist in the same physical object. I perceive the one, you perceive the other. The trouble with this suggestion is that much of the detail of the Protagorean/Heracleitean position in 151184 seems to be generated by Protagoras' desire toavoidcontradiction. If Cornford thinks that Protagoras isnotconcerned to avoid contradicting himself, then he has a huge task of reinterpretation ahead of him.Rather, perhaps, the point of the argument is this: Neither The wind in itself is cold nor The wind in itself is warm is true. If we had grounds for affirming either, we would have equally good grounds for affirming both; but the conjunction The wind in itself is cold and the wind in itself is warm is a contradiction. This contradiction, says Protagoras, obliges us to give up all talk about the wind in itself, and switch to relativised talk about the wind as it seemsto meorto you,etc. (The same contradiction pushes the Plato of theRepublicin the opposite direction: it leads him to place no further trust inanyrelativised talk, precisely because such talk cannot get us beyond such contradictions.)So we have moved from D1, to Hm, to PS. At 152c8152e1 Socrates adds that, in its turn, PS entails Heracleitus' view that All is flux, that there are no stably existingobjectswith stably enduringqualities.The reason given for this is the same thought as the one at the centre of the cold-wind argument: that everything to which any predicate can be applied, according to one perception, can also have the negation of that predicate applied to it, according to an opposite perception with equally good credentials.After a passage (152e1153d5) in which Socrates presents what seem to be deliberately bad arguments, eight of them, for Heracleitus' flux thesis, Socrates notes three shocking theses which the flux theory implies:1. Qualities have no independent existence in time and space (153d6-e1).2. Qualities do not exist except in perceptions of them (153e3154a8).3. (The dice paradox:) changes in a thing's qualities are not so much changes in that thing as in perceptions of that thing (154a9155c6).These shocking implications, Socrates says, give the phenomenal subjectivist his reason to reject the entire object/quality metaphysics, and to replace it with a metaphysics of flux.In 155c-157c the flux theory is used to develop a Protagorean/Heracleitean account of perception, to replace accounts based on the object/property ontology of common sense. Socrates notes the subversive implications of the theory of flux for the meaningfulness and truth-aptness of most of our language as it stands. (He returns to this point at 183a-b.) The ontology of the flux theory distinguishes kinds of process (kinsis), i.e., of flux, in two ways: as fast or slow, and as active or passive. Hence there are four such processes. On these the flux theory's account of perception rests.A rather similar theory of perception is given by Plato inTimaeus45b-46c, 67c-68d. This fact has much exercised scholars, since it relates closely to the question whether Plato himself accepts the flux theory of perception (cp.Theaetetus157c5). The question is important because it connects with the question of whether the Revisionist or Unitarian reading of 151187 is right. (For more on this issue, see Cornford 1935 (4950); Crombie 1963, II (2122); Burnyeat 1990 (1718); McDowell 1973 (139140), Chappell 2005 (7478).)At 157c-160c Socrates states a first objection to the flux theory. This asks how the flux theorist is to distinguish false (deceptive) appearances such as dreams from the true (undeceptive) appearances of the waking world. The flux theorist's answer is that such appearances should not be described as true and false appearances to the same person. Rather they should be described as different appearances to different people. According to the flux theorist, we have the same person if and only if we have the same combination of a perception and a perceiving (159c-d). So there is no need to call any appearancesfalse. Thus we preserve the claim that all appearances are truea claim which must be true if knowledge is perception in the sense that Socrates has taken that definition.160b-d summarises the whole of 151-160. Socrates shows how the exploration of Theaetetus' identification of knowledge with perception has led us to develop a whole battery of views: in particular, a Protagorean doctrine of the incorrigibility of perception, and a Heracleitean account of what perception is. Thus perception has one of the two marks of knowledge, infallibility (Cornford 1935, 58); and, if we can accept Protagoras' identification of what appears to me with what is, ignoring the addition for me and the distinction between being and becoming, the case will be complete.6.3 The Refutation of the Thesis that Knowledge is Perception: 160e5186e12160e marks the transition from the statement and exposition of the definition of knowledge as perception (D1), to the criticism and eventual refutation of that definition.Scholars have divided about the overall purpose of 160e-186e. Mostly they have divided along the lines described in section 3, taking either a Revisionist or a Unitarian view of Part One of theTheaetetus.Revisionists say that the target of the critique of 160e-186e is everything that has been said in support and development of D1 ever since 151. Unitarians argue that Plato's criticism of D1 in 160e-186e is more selective. Obviously his aim is to refute D1, the equation of knowledge with perception. But that does not oblige him to reject the account of perception that has been offered in support of D1. And Plato does not reject this account: he accepts it.Thus the Unitarian Cornford argues that Plato is not rejecting the Heracleitean flux theory of perception. He is rejecting only D1's claim thatknowledgeis that sort of perception. It remains possible that perception is just as Heracleitus describes it. Likewise, Cornford suggests, the Protagorean doctrine that man is the measure of all things is true provided it is taken to mean only all thingsthat we perceive.If some form of Unitarianism is correct, an examination of 160186 should show that Plato's strategy in the critique of D1 highlights two distinctions:1. A distinction between the claim thattheobjects of perceptionare in flux, and the claim thateverythingis in flux.2. A distinction between bare sensory awareness, and judgement on the basis of such awareness.One vital passage for distinction (1) is 181b-183b. If Unitarianism is right, this passage should be an attack on the Heracleitean thesis thateverythingis in flux, but not an attack on the Heracleitean thesis thatthe objects of perceptionare in flux. According to Unitarians, the thesis that the objects of perception are in flux is a Platonic thesis too. Readers should ask themselves whether this is the right way to read 181b 183b.Distinction (2) seems to be explicitly stated at 179c. There also seems to be clear evidence of distinction (2) in the final argument against D1, at 184187. Distinction (2) is also at work, apparently, in the discussion of some of the nine objections addressed to the Protagorean theory. Some of these objections can plausibly be read as points about the unattractive consequences of failing to distinguish the Protagorean claim that bare sense-awareness is incorrigible (as the Unitarian Plato agrees) from the further Protagorean claim thatjudgements aboutsense-awareness are incorrigible (which the Unitarian Plato denies).The criticism of D1 breaks down into twelve separate arguments, interrupted by the Digression (172c-177c: translated and discussed separately in section 6d). There is no space here to comment in detail on every one of these arguments, some of which, as noted above, have often been thought frivolous or comically intended (cp. 152e1153d5). Some brief notes on the earlier objections will show what the serious point of each might be.The first objection to Protagoras (160e-161d) observes that if all perceptions are true, then there is no reason to think that animal perceptions are inferior to human ones: a situation which Socrates finds absurd.If this objection is really concerned with perceptions strictly so called, then it obviously fails. Protagoras just accepts this supposedly absurd consequence; and apparently he is right to do so. If we consider animals and humans just as perceivers, there is no automatic reason to prefer human perceptions. Many animal perceptions aresuperiorto human perceptions (dogs' hearing, hawks' eyesight, dolphins' echolocatory ability, most mammals' sense of smell, etc.), and the Greeks knew it, cf. Homer's commonplace remarks about far-sighted eagles, or indeed Aristotle, in theEudemian Ethics, 1231a56. The objection works much better rephrased as an objection aboutjudgements aboutperceptions, rather than aboutperceptionsstrictly so called. Humans are no more and no lessperceiversthan pigs, baboons, or tadpoles. But they are different in their powers of judgement about perceptions.This distinction between arguments against a Protagorean view about perception and a Protagorean view about judgement about perception is relevant to the second objection too (161d-162a). This objection (cp.Cratylus386c) makes the point that Protagoras' theory implies that no one is wiser than anyone else. Notably, the argument does not attack the idea thatperceptionis infallible. Rather, it attacks the idea that the opinion or judgement that anyone formson the basis ofperception is infallible (161d3). (This is an important piece of support for Unitarianism: cp. distinction (2) above.)A third objection to Protagoras' thesis is very quickly stated in Socrates' two rhetorical questions at 162c26. Since Protagoras' thesis implies that all perceptions are true, it not only has the allegedly absurd consequence that animals' perceptions are not inferior to humans. It also has the consequence that humans' perceptions are not inferior to the gods'. This consequence too is now said to be absurd.As with the first two objections, so here. If we consider divinities and humans just as perceivers, there is no automatic reason to prefer divine perceptions, and hence no absurdity. Plato may well want us to infer that the Greek gods are not different just in respect of beingperceiversfrom humans. But theyaredifferent in their powers of judgement about perceptions.The next four arguments (163a-168c) present counter-examples to the alleged equivalence of knowledge and perception. The fourth observes that, if perception = knowledge, then anyone who perceives an utterance in a given language should have knowledge of that utterance, i.e., understand itwhich plainly doesn't happen. The fifth raises a similar problem about memory and perception: remembering things isknowingthem, but notperceivingthem. The sixth (the covered eye) objection contrastsnot perceivingan object (in one sensory modality) withnot knowing it. If perception = knowledge, seeing an object with one eye and not seeing it with the other would appear to be a case of the contradictory state of both knowing it and not knowing it. The seventh points out that one can perceive dimly or faintly, clearly or unclearly, but that these adverbial distinctions do not apply to ways of knowingas they must if knowingisperceiving.In 165e4168c5, Socrates sketches Protagoras's response to these seven objections. Protagoras makes two main points. First, he can meet some of the objections by distinguishing types and occasions of perception. Second, teaching as he understands it is not a matter of getting the pupil to have true rather than false beliefs. Since there are no false beliefs, the change that a teacher can effect is not a change from false belief to true belief or knowledge. Rather, Protagoras' model of teaching is atherapeuticmodel. What a good teacher does, according to him, is use arguments (or discourses:logoi) as a good doctor uses drugs, to replace the state of the soul in which bad things are and appear with one in which good things are and appear. While all beliefs aretrue, not all beliefs arebeneficial.A difficulty for Protagoras' position here is that, if all beliefs are true, then all beliefs about which beliefs are beneficial must be true. But surely, some beliefs about which beliefs are beneficial contradict other beliefs about which beliefs are beneficial; especially if some people are better than others at bringing about beneficial beliefs. (For example, no doubt Plato's and Protagoras' beliefs conflict at this point.) This means that Protagoras' view entails a contradiction of the same sort as the next objectionthe famousperitropseems to be meant to bring out.Theperitrop(table-turning) objection (171a-b) is this. Suppose I believe, as Protagoras does, that All beliefs are true, but also admit that There is a belief that Not all beliefs are true. If all beliefs are true, the belief that Not all beliefs are true must be true too. But if that belief is true, then by disquotation, not all beliefs are true. So I refute myself by contradicting myself; and the same holds for Protagoras.The validity of the objection has been much disputed. Burnyeat, Denyer and Sedley all offer reconstructions of the objection that make it come out valid. McDowell and Bostock suggest that although the objection does not prove what it is meant to prove (self-contradiction), it does prove a different point (about self-defeat) which is equally worth making.Socrates' ninth objection presents Protagoras' theory with a dilemma. If the theory is completely general in its application, then it must say that not only what counts asjusticein cities, but also whatbenefitscities, is a relative matter. As Protagoras has already admitted (167a3), it is implausible to say that benefit is a relative notion. But the alternative, which Protagoras apparently prefers, is a conceptual divorce between the notions of justice and benefit, which restrict the application of Protagoras' theory to the notion of justice. Socrates obviously finds this conceptual divorce unattractive, though he does not, directly, say why. Instead, he offers us the Digression.6.4 The Digression: 172c1177b7An obvious question: what is the Digression for? One answer (defended in Chappell 2004, ad loc.) would be that it is a critique of the society that produces the conceptual divorce between justice and benefit that has just emerged. Socrates draws an extended parallel between two types of character, the philosophical man and the man of rhetoric, to show that it is better to be the philosophical type.The Digression is philosophically quite pointless, according to Ryle 1966: 158. Less dismissively, McDowell 1976: 174 suggests that the Digression serves a purpose which, in a modern book, might be served by footnotes or an appendix. Similarly, Cornford 1935 (83) suggests that Plato aims to give the reader some references for anti-relativist arguments that he presents elsewhere: To argue explicitly against it would perhaps take him too far from the original topic of perception. Instead, he inserts [the Digression], which contains allusions to such arguments in other works of his.Perhaps the Digression paints a picture of what it is like tolivein accordance with the two different accounts of knowledge, the Protagorean and the Platonist, that Plato is comparing. Thus the Digression shows us what is ethically at stake in the often abstruse debates found elsewhere in theTheaetetus. Its point is that we can't make a decision about what account of knowledge to accept without making all sorts of other decisions, not only about the technical, logical and metaphysical matters that are to the fore in the rest of theTheaetetus, but also about questions of deep ethical significance. So, for instance, it can hardly be an accident that, at 176c2, the difference between justice and injustice is said to be a difference between knowledge (gnsis) and ignorance (agnoia).Another common question about the Digression is: does it introduce or mention the Platonic Forms? Certainly the Digression uses phrases that are indisputably part of the Middle-Period language for the Forms. If Plato uses the language of the theory of Forms in a passage which is admitted on all sides to allude to the themes of theRepublic, it strains credulity to imagine that Plato is not intentionally referring to the Forms in that passage.On the other hand, as the Revisionist will point out, theTheaetetusdoes not seem todomuch with the Forms that are thus allegedly introduced. But perhaps it would undermine the Unitarian reading of theTheaetetusif the Formswerepresent in the Digression in the role of paradigm objects of knowledge. For the Unitarian reading, at least on the version that strikes me as most plausible, says that the aim of theTheaetetusis to show that, in the end, we cannot construct a theory of knowledge without the Forms--a claim which is to be proved by trying and failing, three times, to do so. So if the Forms were there in the Digression, perhaps that would be a case of giving the game away.6.5 Last Objection to Protagoras: 177c6179b5After the Digression Socrates returns to criticising Protagoras' relativism. His last objection is that there is no coherent way of applying Protagoras' relativism to judgements about the future.How might Protagoras counter this objection? Protagoras has already suggested that the past may now be no more than whatever I now remember it to have been (166b). Perhaps he can also suggest that the future is now no more than I now believe it will be. No prediction is ever proved wrong, just as no memory is ever inaccurate. All that happens is it seems to one self at one time that somethingwill betrue (orhas beentrue), and seems to another self at another time that something differentistrue.But these appeals to distinctions between Protagorean selvesfuture or pastdo not help. Suppose we grant to Protagoras that, when I make a claim about how the future will be, this claim concerns how things will befor my future self. It is just irrelevant to add that my future self and I are different beings. Claims about the future still have a form that makes them refutable bysomeone'sfuture experience. If I predict on Monday that on Tuesday my head will hurt, that claim is falsified either if I have no headache on Tuesday, or if, on Tuesday, there is someone who is by convention picked out as my continuant whose head does not hurt.Similarly with the past. Suppose I know on Tuesday that on Monday I predicted that on Tuesday my head would hurt. It is no help against the present objection for me to reflect, on Tuesday, that I am a different person now from who I was then. My Monday-self can only have meant either thathishead would hurt on Tuesday, which was a false belief on his part if he no longer exists on Tuesday; or else that the Tuesday-self would have a sore head. But if the Tuesday-self has no sore head, then my Monday-self made a false prediction, and so must have had a false belief. Either way, the relativist does not escape the objection.Moreover, this defence of Protagoras does not evade the following dilemma. Either what I mean by claiming (to take an example of Bostock's) that The wine will taste raw to me in five years' time is literally that. Or else what I mean is just It seems to methat the wine will taste raw to me in five years' time.Suppose I mean the former assertion. If the wine turns out not to taste raw five years hence, Protagoras has no defence from the conclusion that I made a false prediction about how things would seem to me in five years. Or suppose I meant the latter assertion. Then I did not make aprediction, strictly speaking, at all; merely a remark about what presently seems to me. Either way, Protagoras loses.6.6 Last Objection to Heracleitus: 179c1183c2Socrates argues that if Heracleitus' doctrine of flux is true, then no assertion whatever can properly be made. Therefore (a) Heracleitus' theory of flux no more helps to prove that knowledgeisperception than that knowledgeisnotperception, and (b) Heracleiteans cannot coherently say anything at all, not even to state their own doctrine.There are two variants of the argument. On the first of these variants, evident in 181c2-e10, Socrates distinguishes justtwokinds of flux or process, namely qualitative alteration and spatial motion, and insists that the Heracleiteans are committed to saying that both are continual. On the second variant, evident perhaps at 182a1, 182e45, Socrates distinguishes indefinitely many kinds of flux or process, not just qualitative alteration and motion through space, and insists that the Heracleiteans are committed to saying thateverykind of flux is continual.Now the view that everything is always changing in every way might seem a rather foolish view to take about everyday objects. But, as 182a2-b8 shows, the present argument is not about everyday objects anyway. Plato does not apply his distinction between kinds of change to every sort of object whatever, including everyday objects. He applies it specifically to the objects (if that is the word) of Heracleitean metaphysics. These items are supposed by the Heracleitean to be the reality underlying all talk of everyday objects. It is at the level of these Heracleitean perceivings and perceivers that Plato's argument against Heracleitus is pitched. And it is not obviously silly to suppose that Heracleitean perceivings and perceivers are constantly changing in every way.The argument that Socrates presents on the Heracleiteans' behalf infers from Everything is always changing in every way that No description of anything is excluded. How does this follow? McDowell 1976: 1812 finds the missing link in the impossibility ofidentifications. We cannot (says McDowell) identify a moving sample of whiteness, or of seeing,any longeronce it has changed into some other colour, or perception.But this only excludesreidentifications: presumably I can identify the moving whiteness or the moving seeinguntilit changes, even if this only gives me an instant in which to identify it. This point renders McDowell's version, as it stands, an invalid argument. If it is on his account possible to identify the moving whitenessuntil it changes, then it is on his account possible to identify the moving whiteness. But if that is possible, then his argument contradicts itself: for it goes on to deny this possibility.Some other accounts of the argument also commit this fallacy. Compare Sayre's account (1969: 94): If no statement, either affirmative or negative, can remain true for longer than the time taken in its utterance, then no statement can be treated as either true or false, and the cause of communicating with one's fellow beings must be given up as hopeless.Sayre's argument aims at the conclusion No statement can be treated as either true or false. But Sayre goes via the premiss Any statement remains true no longer than the time taken in its utterance. If there are statements whicharetrue, even if they are not true for very long, it is not clear why these statements cannot betreatedastrue, at least in principle (and in practice too, given creatures with the right sensory equipment and sense of time).McDowell's and Sayre's versions of the argument also face the following objection. It is obvious how, given flux, a present-tense claim like ItemXis present can quickly cease to be true, because e.g., ItemYis present comes to replace it. But it isn't obvious why flux should exclude the possibility of past-tense statements like ItemXflowed into itemYbetweent1andt2, or of tenseless statements like ItemXis present att1, itemYis present att2. As Bostock 1988: 1056 points out, So long as we do have a language with stable meanings, and the ability to make temporal distinctions, there is no difficulty at all about describing an ever-changing world.So long as: to make the argument workable, we may suggest that its point is that themeanings of wordsare exempt from flux. If meanings are not in flux, and if we have access to those meanings, nothing stops us from identifying the whiteness at least until it flows away. But if meanings are in flux too, we will have the result that the argument against Heracleitus actually produces at 183a5: anything at all will count equally well as identifying or not identifying the whiteness. Unless we recognise some class of knowable entities exempt from the Heracleitean flux and so capable of standing as the fixed meanings of words, no definition of knowledge can be any more true than its contradictory. Plato is determined to make us feel the need of his Forms without mentioning them (Cornford 1935, 99).6.7 The Final Refutation of D1: 183c4187a8Socrates completes his refutation of the thesis that knowledge is perception by bringing a twelfth and final objection, directed against D1 itself rather than its Protagorean or Heracleitean interpretations. This objection says that the mind makes use of a range of concepts which it could not have acquired, and which do not operate, through the senses: e.g., existence, sameness, difference. So there is a part of thought, and hence of knowledge, which has nothing to do with perception. Therefore knowledge is not perception.Unitarians and Revisionists will read this last argument against D1 in line with their general orientations. Unitarians will suggest that Socrates' range of concepts common to the senses is a list of Forms. They will point to the similarities between the image of the senses as soldiers in a wooden horse that Socrates offers at 184d1 ff., and the picture of a Heracleitean self, existing only in its awareness of particular perceptions, that he drew at 156160.Revisionists will retort that there are important differences between the Heracleitean self and the wooden-horse self, differences that show that Heracleiteanism is no longer in force in 184187. They will insist that the view of perception in play in 184187 is Plato's own non-Heracleitean view of perception. Thus Burnyeat 1990: 55-56 argues that, since Heracleiteanism has been refuted by 184, the organs and subjects dealt with [in the Wooden Horse passage] are the ordinary stable kind which continue in being from one moment to the next. On the other hand, notice that Plato's equivalent for Burnyeat's organs and subjects is the single wordaisthseis(184d2). On its own, the word can mean either senses or sensings; but it seems significant that it was the word Plato used at 156b1 for one of the two sorts of Heracleitean offspring. Plato speaks of theaisthseisconcealed as if within a Wooden Horse aspollai tines(184d1), indefinitely many. But while there are indefinitely many Heracleiteansensings, there are not, of course, indefinitely manysenses. Indeed even the claim that we havemanysenses (pollai), rather thanseveral(enioi,tines), does not sound quite right, either in English or in Greek. This is perhaps why most translators, assuming thataisthseismeans senses, put a number of senses forpollai tines aisthseis. Perhaps this is a mistake, and whataisthseismeans here is Heracleitean sensings. If so, this explains how theaisthseisinside any given Wooden Horse can bepollai tines.If theaisthseisin the Wooden Horse are Heracleiteansensings, not ordinary, un-Heracleiteansenses, this supports the Unitarian idea that 184187 is contrasting Heracleitean perceiving of particulars with Platonic knowing of the Forms (or knowing of particularsvia, andin terms of, the Forms).Another piece of evidence pointing in the same direction is the similarity between Plato's list of the common notions atTheaetetus186a and closely contemporary lists that he gives of the Forms, such as the list of Forms (likeness,multitude,restand their opposites) given atParmenides129d, with ethical additions atParmenides130b. There are also themegista gen(greatest kinds) ofSophist254b-258e (being,sameness,otherness,restandchange); though whether thesegenare Forms is controversial.7. Second Definition (D2): Knowledge is True Judgement: 187b-201c151187 has considered and rejected the proposal that knowledge is perception. Sometimes in 151187 perception seems to mean immediate sensory awareness; at other times it seems to mean judgements madeaboutimmediate sensory awareness. The proposal that Knowledge is immediate sensory awareness is rejected as incoherent: Knowledge is not to be found in our bodily experiences, but in our reasonings about those experiences (186d2). The proposal that Knowledge is judgement about immediate sensory awareness raises the questionhowjudgements, or beliefs, can emerge from immediate sensory awareness. Answering this question is the main aim in 187201.Empiricists claim that sensation, which in itself has no cognitive content, is the source of all beliefs, which essentially have cognitive contentwhich are by their very nature candidates for truth or falsity. So unless we can explain how beliefs can be true or false, we cannot explain how there can be beliefs at all. Hence Plato's interest in the question of false belief. What Plato wants to show in 187201 is that there is no way for the empiricist to construct contentful belief from contentless sensory awareness alone. The corollary is, of course, that we need something else besides sensory awareness to explain belief. In modern terms, we need irreduciblesemantic properties.In Plato's terms, we need the Forms.In pursuit of this strategy of argument in 187201, Plato rejects in turn five possible empiricist explanations of how there can be false belief. In the First Puzzle (188a-c) he proposes a basic difficulty for any empiricist. Then he argues that no move available to the empiricist circumvents this basic difficulty, however much complexity it may introduce (the other four Puzzles: 188d-201b). The Fifth Puzzle collapses back into the Third Puzzle, and the Third Puzzle collapses back into the First. The proposal that gives us the Fourth Puzzle is disproved by the counter-examples that make the Fifth Puzzle necessary. As for the Second Puzzle, Plato deploys this to show how empiricism has the disabling drawback that it turns an outrageous sophistical argument into a valid disproof of the possibility of at least some sorts of false belief.Thus 187201 continues the critique of perception-based accounts of knowledge that 151187 began. Contrary to what somefor instance Cornfordhave thought, it is no digression from the main path of theTheaetetus. On the contrary, the discussion of false belief is the most obvious way forward.As Plato stresses throughout the dialogue, it is Theaetetus who is caught in this problem about false belief. It is not Socrates, nor Plato. There is clear evidence atPhilebus38c ff. that false belief (at least of some sorts) was no problem at all to Plato himself (at least at some points in his career). Plato's question is not How on earth can there be false judgement? Rather it is What sort of background assumptions about knowledge must Theaetetus be making, given that he is puzzled by the question how there can be false judgement?Is it only false judgements ofidentitythat are at issue in 187201, or is itanyfalse judgement? One interpretation of 187201 says that it is only about false judgements of misidentification. Call this viewmisidentificationism. The main alternative interpretation of 187201 says that it is about any and every false judgement. Call this viewanti-misidentificationism. The present discussion assumes the truth of anti-misidentificationism; see Chappell 2005: 154-157 for the arguments.I turn to the detail of the five proposals about how to explain false belief that occupy Stephanus pages 187 to 200 of the dialogue.7.1 The Puzzle of Misidentification: 187e5188c8The first proposal about how to explain the possibility of false belief is the proposal that false belief occurs when someone misidentifies one thing as another. To believe or judge falsely is to judge, for some two objectsO1andO2, thatO1isO2.How can such confusions even occur? Plato presents a dilemma that seems to show that they can't. The objects of the judgement,O1andO2, must either be known or unknown to the judgerx. Suppose one of the objects, sayO1, is unknown tox. In that case,O1cannot figure inx's thoughts at all, sincexcan only form judgements using objects that he knows. So ifO1is not an object known tox,xcannot makeanyjudgement aboutO1.A fortiori,then,xcan make nofalsejudgement aboutO1either.If, on the other hand, bothO1andO2are known tox, thenxcan perhaps makesomejudgements aboutO1andO2; but not the false judgement that O1isO2. IfxknowsO1andO2,xmust know thatO1isO1andO2isO2, and that it would be a confusion to identify them. So apparently false belief is impossible if the judger does not know bothO1andO2; but also impossible if he does know bothO1andO2.I cannot mistakeXforYunless I am able to formulate thoughts aboutXandY. But I will not be able to formulate thoughts aboutXandYunless I amacquaintedwithXandY. Being acquainted withXandYmeansknowingXandY; and anyone who knowsXandYwill not mistake them for each other.Why think this a genuine puzzle? There seem to be plenty of everyday cases where knowing some thing in no way prevents us from sometimes mistaking that thing for something else. One example in the dialogue itself is at 191b (cp. 144c5). It is perfectly possible for someone who knows Socrates to see Theaetetus in the distance, and wrongly think that Theaetetus is Socrates. The First Puzzle does not even get off the ground, unless we can see why our knowledge ofXandYshould guarantee us against mistakes aboutXandY. Who is the puzzle of 188a-c supposed to be a puzzlefor?Some authors, such as Bostock, Crombie, McDowell, and White, think that Plato himself is puzzled by this puzzle. Thus Crombie 1963: 111 thinks that Plato advances the claim that any knowledge at all of an objectOis sufficient for infallibility aboutObecause he fails to see the difference between being acquainted withX and being familiar withX. But to confuse knowingeverythingaboutXwith knowing enough aboutXto use the name X is really a very simple mistake. Plato would not be much of a philosopher if he made this mistake.If (as is suggested in e.g. Chappell 2004, ad loc.) 187201 is an indirect demonstration that false belief cannot be explained by empiricism (whether this means a developed philosophical theory, or the instinctive empiricism of some people's common sense), then it is likely that the First Puzzle states the basic difficulty for empiricism, to which the other four Puzzles look for alternative solutions. The nature of this basic difficulty is not fully, or indeed at all, explained by the First Puzzle. We have to read on and watch the development of the argument of 187201 to see exactly what the problem is that gives the First Puzzle its bite.7.2 Second Puzzle About False Belief: Believing What is Not: 188c10189b9The second proposal says that false judgement is believing or judgingtam onta, things that are not or what is not. Socrates observes that if what is not is understood as it often was by Greek thinkers, as meaning nothing, then this proposal leads us straight into the sophistical absurdity that false beliefs are the same thing as beliefs about nothing (i.e., contentless beliefs). But there can be no beliefs about nothing; and there are false beliefs; so false belief isn't the same thing as believing what is not.Some think the Second Puzzle a mere sophistry. Bostock 1988: 165 distinguishes two versions of the sophistry: On one version, to believe falsely is to believe what is not just by itself; on the other version, it is to believe what is not about one of the things which are. The argument of the first version, according to Bostock, is just that there is no such thing as what is not (the case); it is a mere nonentity. But just as you cannot perceive a nonentity, so equally you cannot believe one either. Bostock proposes the following solution to this problem: We may find it natural to reply to this argument by distinguishing propositions [from] facts, situations, states of affairs, and so on. Then we shall say that the things that are believed are propositions, not facts so a false belief is not directed at a non-existent.This raises the question whether a consistent empiricist can admit the existence of propositions. At least one great modern empiricist, Quine 1953: 1567, thinks not. Plato agrees: he regards a commitment to the existence of propositions as evidence ofPlatonism,acceptance of the claim that abstract objects (and plenty of them) genuinely exist. So an explanation of false judgement that invoked entities called propositions would be unavailable to the sort of empiricist that Plato has in his sights.Bostock's second version of the puzzle makes it an even more transparent sophistry, turning on a simple confusion between the is of predication and the is of existence. As pointed out above, we can reasonably ask whether Plato made this distinction, or made it as we make it.If the structure of the Second Puzzle is really as Bostock suggests, then the Second Puzzle is just the old sophistry about believing what is not (cp. Parmenides DK 29B8, Euthydemus283e ff.,Cratylus429d,Republic477a,Sophist263e ff.). Moreover, on this interpretation of the Second Puzzle, Plato is committed, in his own person and with full generality, to accepting (at least provisionally) a very bad argument for the conclusion that there can be no false belief. It would be nice if an interpretation of the Second Puzzle were available that saw it differently: e.g., as accepted by him only in a context where special reasons make the Second Puzzle very plausible in that context.One such interpretation is defended e.g., by Burnyeat 1990: 78, who suggests that the Second Puzzle can only work if we accept the scandalous analogy between judging what is not and seeing or touching what is not there to be seen or touched: A model on which judgements relate to the world in the same sort of unstructured way as perceiving or (we may add) naming, will tie anyone in knots when it comes to the question What is a false judgement the judgement/ name of?. The only available answer, when the judgement is taken as an unstructured whole, appears to be: Nothing.Notice that it is the empiricist who will most naturally tend to rely on this analogy. It is the empiricist who finds it natural to assimilate judgement and knowledge to perception, so far as he can. So we may suggest that the Second Puzzle is a mere sophistry for any decent account of false judgement, but a good argument against the empiricist account of false judgement that Plato is attacking. The moral of the Second Puzzle is that empiricism validates the old sophistrybecauseit treats believing or judging as too closely analogous to seeing: 188e47. For empiricism judgement, and thought in general, consists in awareness of the ideas that are present to our minds, exactlyasthey are present to our minds. It cannot consist in awareness of those ideasas they are not; because (according to empiricism) we are immediately and incorrigibly aware of our own ideas, it can only consist in awareness of those ideasas they are. Nor can judgement consist in awareness of ideas that arenotpresent to our minds, for (according to empiricism) what is not present to our minds cannot be a part of our thoughts. Still less can judgement consist in awareness of ideas that do not exist at all.The old sophists took false belief as judging what is not; they then fallaciously slid from judging what is not, to judging nothing, to not judging at all, and hence concluded that no judgement that was ever actually made was a false judgement. The empiricism that Plato attacks not only repeats this logical slide; it makes it look almost reasonable. The point of the Second Puzzle is to draw out this scandalous consequence.7.3 Third Puzzle About False Belief:Allodoxia: 189b10190e4Literally translated, the third proposal about how to explain the possibility of false belief says that false belief occurs when someone exchanges (antallaxamenos) in his understanding one of the things that are with another of the things that are, and saysis (189b12-c2).Perhaps the best way to read this very unclear statement is as meaning that the distinctive addition in the third proposal is the notion ofinadvertency. The point of Socrates' argument is that this addition does not help us to obtain an adequate account of false belief because thought (dianoia) has to be understood as an inner process, with objects that we are always fully and explicitly conscious of. If we are fully and explicitly conscious of all the objects of our thoughts, and if the objects of our thoughts are as simple as empiricism takes them to be, there is simply no room for inadvertency. But without inadvertency, the third proposal simply collapses back into the first proposal, which has already been refuted.The empiricist conception of knowledge that Theaetetus unwittingly brings forth, and which Socrates is scrutinising, takes the objects of thought to be simple mental images which are either straightforwardly available to be thought about, or straightforwardly absent. The First Puzzle showed that there is a general problem for the empiricist about explaining how such images can be confused with each other, or indeed semantically conjoined in any way at all. The Second Puzzle showed that, because the empiricist lacks clear alternatives other than that someone shouldhavea mental image orlackit, he is wide open to the sophistical argument which identifiesbelievingwithhaving a mental image, and then identifiesbelieving what iswithhaving a mental image, tooand so proves the impossibility of false belief. The Third Puzzle restricts itself (at least up to 190d7) to someone whohasthe requisite mental images, and adds the suggestion that he manages to confuse them by a piece of inadvertency. Socrates' rejoinder is that nothing has been done to showhowthere can be inadvertent confusions of things that are as simple and unstructured, and as simply grasped ornotgrasped, as the empiricist takes mental images to be. Just as speech is explicitouterdialogue, so thought is explicitinnerdialogue. What the empiricist needs to do to show the possibility of such a confusion is to explain how, on his principles, either speech or thought can fail to be fully explicit and fully in touch with its objects, if it is in touch with them at all.In the discussion of the Fourth and Fifth Puzzles, Socrates and Theaetetus together work out the detail of two empiricist attempts to explain just this. It then becomes clearer why Plato does not think that the empiricist can explain the difference between fully explicit and not-fully-explicit speech or thought. Plato thinks that, to explain this, we have to abandon altogether the empiricist conception of thought as the concatenation (somehow) of semantically inert simple mental images. Instead, we have to understand thought as the syntactic concatenation of the genuine semantic entities, theForms. Mistakes in thought will then be comprehensible as mistakes either about the logical interrelations of the Forms, or about the correct application of the Forms to the sensory phenomena.7.4 Fourth Puzzle About False Belief: the Wax Tablet: 190e5196c5The Wax Tablet passage offers us a more explicit account of the nature of thought, and its relationship with perception. The story now on offer says explicitly that perception relates to thought roughly as Humean impressions relate to Humean ideas (191d; compare Hume,First EnquiryII). The objects of perception, as before, are a succession of constantly-changing immediate awarenesses. The objects of thought, it is now added, are those objects of perception to which we have chosen to give a measure of stability by imprinting them on the wax tablets in our minds. (The image of memory as writing in the mind had currency in Greek thought well before Plato's time: see e.g. Aeschylus,Eumenides275.)This new spelling-out of the empiricist account of thought seems to offer new resources for explaining the possibility of false belief. The new explanation can say that false belief occurs when there is a mismatch, not between two objects ofthought, nor between two objects ofperception, but between one object of each type.This proposal faces a simple and decisive objection. No one disputes that there are false beliefs thatcannotbe explained as mismatches of thought and perception: e.g., false beliefs about arithmetic. The Wax Tablet does not explain how such false beliefs happen; indeed it entails that theycan'thappen. Such mistakes are confusions of two objects of thought, and the Wax Tablet model does not dispute the earlier finding that there can be no such confusions. So the Wax Tablet model fails.There is of course plenty more that Platocouldhave said in criticism of the Wax Tablet model. Most obviously, he could have pointed out the absurdity of identifying any number with any individual'sthoughtof that number (195e9 ff.); especially when the numerical thought in question is no more than an ossified perception. In the present passage Plato is content to refute the Wax Tablet by the simplest and shortest argument available: so he does not make this point. But perhaps the point is meant to occur to the reader; for the same absurdity reappears in an even more glaring form in the Aviary passage.7.5 Fifth Puzzle About False Belief: the Aviary: 196d1200d4If we had a solution to the very basic problem about how the empiricist can get any content at all out of sensation, then the fourth proposal might show how the empiricist could explain false belief involving perception. The fifth and last proposal about how to explain the possibility of false belief attempts to remedy the fourth proposal's incapacitywhich Plato says refutes it, 196c57to deal with cases of false belief involving no perception, such as false arithmetical beliefs.It attempts this by deploying a distinction between knowledge that someone merelyhas(latent knowledge) and knowledge that he is actuallyusing(active knowledge).(Perhaps Plato is now exploring the intermediate stages between knowing and not knowing mentioned at 188a23.) The suggestion is that false belief occurs when someone wants to use some item of latent knowledge in his active thought, but makes a wrong selection from among the items that he knows latently.If this proposal worked it would cover false arithmetical belief. But the proposal does not work, because it is regressive. If there is a problem about the very possibility of confusing two things, it is no answer to this problem to suppose that for each thing there is a corresponding item of knowledge, and that what happens when twothingsare confused is really that the two correspondingitemsofknowledgeare confused (200a-b).The Aviary rightly tries to explain false belief by complicating our picture of belief. But it complicates in the wrong way and the wrong place. It is no help to complicate the story by throwing in further objects of the same sort as the objects that created the difficulty about false belief in the first place. What is needed is a different sort of object for thought: a kind of object that can be thought of under different aspects (say, as the sum of 5 and 7, or as the integer 12). There are no such aspects to the items of knowledge that the Aviary deals in. As with the conception of the objects of thought and knowledge that we found in the Wax Tablet, it is this lack of aspects that dooms the Aviary's conception of the objects of knowledge too. Like the Wax Tablet, the Aviary founders on its own inability to accommodate the point that thought cannot consist merely in the presentation of a series of inert objects of thought. Whether these objects of thought are mental images drawn from perception or something else, the thinking is not so much in the objects of thought as in what isdonewith those objects (186d24).We may illustrate this by asking: When the dunce who supposes that 5 + 7 = 11 decides to activate some item of knowledge to be the answer to What is the sum of 5 and 7?,whichitem of knowledge does he thus decide to activate? At first only two answers seem possible: either he decides to activate 12, or he decides to activate 11. If he decides to activate 12, then we cannot explain the fact that what he actually does is activate 11, except by saying that he mistakes the item of knowledge which is 11 for the item of knowledge which is 12. But this mistake is the very mistake ruled out as impossible right at the beginning of the inquiry into false belief (188a-c). Alternatively, if he decides to activate 11, then we have to askwhyhe decides to do this. The most plausible answer to that question is: Because he believes falsely that 5 + 7 = 11. But as noted above, if he has already formed this false belief,withinthe account that is supposed to explain false belief, then a regress looms.In fact, the correct answer to the question Which item of knowledge does the dunce decide to activate? is neither 12 nor 11. It is that numberwhich is the sum of 5 and 7. But this answer does not save the Aviary theorist from the dilemma just pointed out; for it is not available to him. To be able to give this answer, the Aviary theorist would have to be able to distinguish that number which is the sum of 5 and 7 from 12. But since 12is that number which is the sum of 5 and 7, this distinction cannot be made by anyone who takes the objects of thought to be simple in the way that the Aviary theorist seems to.At 199e1 ff. Theaetetus suggests an amendment to the Aviary. This is that we might have items ofignorancein our heads as well as items of knowledge. As Socrates remarks, these ignorance-birds can be confused with knowledge-birds in just the same way as knowledge-birds can be confused with each other. So the addition does not help.7.6 The Final Refutation of D2: 200d5201c7At 200d-201c Socrates argues more directly against D2. He offers a counter-example to the thesis that knowledge is true belief. A skilled lawyer can bring jurymen into a state of true belief without bringing them into a state of knowledge; so knowledge and true belief are different states.McDowell 1976: 2278 suggests that this swift argument contradicts the most characteristic expositions of the Theory of Forms, which indicate that the title knowledge should be reserved for a relation between the mind and the Forms untainted by any reliance on perception. By contrast Plato here tells us, quite unambiguously, that the jury are persuaded into a state of true belief about things which only someone who sees them can know (201b8). This implies that there can be knowledge which is entirely reliant on perception. (One way out of this is to deny that Plato ever thought that knowledge isonlyof the Forms, as opposed to thinking that knowledge isparadigmaticallyof the Forms. For this more tolerant Platonist view about perception see e.g.Philebus58d-62d, andTimaeus27d ff.)The jury argument seems to be a counter-example not only to D2 but also to D3, the thesis that knowledge is true beliefwith an account(provided we allow that the jury have an account).A third problem about the jury argument is that Plato seems to offer two incompatible explanations of why the jury don't know: first that they have only a limited time to hear the arguments (201b3, 172e1); and second that their judgement is second-hand (201b9).8. Third Definition (D3): Knowledge is True Judgement With an Account: 201d-210aTheaetetus' third proposal about how to knowledge is (D3) that it is true belief with an account (meta logou alth doxan).D3 apparently does nothing at all to solve the main problems that D2 faced. Besides the jurymen counter-example just noted, 187-201showed that we could not define knowledge astruebelief unless we had an account offalsebelief. This problem has not just evaporated in 201210. It will remain as long as we propose to define knowledge as true belief plus anything. Significantly, this does not seem to bother Platoas we might expect if Plato is not even trying to offer an acceptable definition of knowledge, but is rather undermining unacceptable definitions.One crucial question aboutTheaetetus201210 is the question whether the argument is concerned with objectual or propositional knowledge. This is a basic and central division among interpretations of the whole passage 201210, but it is hard to discuss it properly without getting into the detail of the Dream Theory: see section 8a.A second question, which arises often elsewhere in theTheaetetus, is whether the argument's appearance ofaporiareflects genuine uncertainty on Plato's part, or is rather a kind of literary device. Is Plato thinking aloud, trying to clarify his own view about the nature of knowledge, as Revisionists suspect? Or is he using an aporetic argument only to smoke out his opponents, as Unitarians think?The evidence favours the latter reading. There are a significant number of other passages where something very like Theaetetus' claim (D3) that knowledge is true belief with an account is not only discussed, but actually defended: for instance,Meno98a2,Phaedo76b56,Phaedo97d-99d2,Symposium202a5-9,Republic534b3-7, andTimaeus51e5. So it appears that, in theTheaetetus, Plato cannot be genuinely puzzled about what knowledge can be. Nor can he genuinely doubt his own former confidence in one version of D3. If he does have a genuine doubt or puzzle of this sort, it is simply incredible that he should say what he does say in 201210 without also expressing it.What Plato does in 201210 is: present a picture (Socrates' Dream) of how things may be if D3 is true (201c-202c); raise objections to the Dream theory which are said (206b12) to be decisive (202c-206c); and present and reject three further suggestions about the meaning oflogos, and so three more versions of D3 (206c-210a). But none of these four interpretations of D3 is Plato's own earlier version of D3, which says that knowledge = true belief with an accountof the reason why the true belief is true. If what Plato wants to tell us inTheaetetus201210 is that he no longer acceptsanyversion of D3, not even his own version, then it is extraordinary that he does not even mention his own version, concentrating instead on versions of D3 so different from Plato's version as to be obviously irrelevant to its refutation.Unitarians can suggest that Plato's strategy is to refute what he takes to be false versions of D3 so as to increase the logical pressure on anyone who rejects Plato's version of D3. In particular, he wants to put pressure on the empiricist theories of knowledge that seem to be the main target of theTheaetetus. What Plato wants to show is, not only that no definition of knowledge except his own, D3, is acceptable, but also that no version of D3 except his own is acceptable.8.1 The Dream of Socrates: 201d8202d7Rather as Socrates offered to develop D1 in all sorts of surprising directions, so now he offers to develop D3 into a sophisticated theory of knowledge. This theory, usually known as the Dream of Socrates or the Dream Theory, posits two kinds of existents, complexes and simples, and proposes that an account means an account of the complexes that analyses them into their simple components. Thus knowledge ofx turns out to mean true belief aboutxwith an account ofxthat analysesxinto its simple components.Taken as a general account of knowledge, the Dream Theory implies that knowledge is only of complexes, and that there can be no knowledge of simples. Socrates attacks this implication.A common question about the Dream Theory is whether it is concerned with objectual or propositional knowledge. Those who take the Dream Theory to be concerned withpropositionalknowledge include Ryle 1990: 2730: from 201 onwards Plato concentrates on know (connatre): [Socrates' Dream] is a logician's theory, a theory about the composition of truths and falsehoods. Those who take the Dream Theory to be concerned withobjectualknowledge include White 1976: 177, and Crombie 1963: II: 4142; also Bostock 1988. A third way of taking the Dream Theory, which may well be the most promising interpretation, is to take it as aLogical Atomism: as a theory which founds an account of propositional structure on an account of the concatenation of simple objects of experience or acquaintance such as sense data.The Logical-Atomist reading of the Dream Theory undercuts the propositional/ objectual distinction. On this reading, the Dream Theory claims that simple, private objects of experience are the elements of the proposition; thus, the Dream Theory isbotha theory about the structure of propositionsanda theory about simple and complex objects. It claims in effect that a proposition's structure is that of a complex object made up out of simple objects, where these simple objects are conceived in the Russellian manner as objects of inner perception or acquaintance, and the complexes which they compose are conceived in the phenomenalist manner as (epistemological and/ or semantic) constructs out of those simple objects.This supposition makes good sense of the claim that we ourselves are examples of complexes (201e2: the primary elements (prta stoikheia) of which we and everything else are composed). If the Dream theorist is a Logical Atomist, he will think that there is a clear sense in which people, and everything else, are composed out of sense data. He will also think that descriptions of objects, too, are complexes constructed in another way out of the immediately available simples of sensation.For such a theorist, epistemology and semantics alike rest upon the foundation provided by the simple objects of acquaintance. Both thought and meaning consist in the construction of complex objects out of those simple objects. Philosophical analysis, meanwhile, consists instating howthe complexes involved in thought and meaning are constructed out of simples. This statement involves, amongst other things, dividing down to and enumerating the (simple) parts of such complexes.What then is the relation of the Dream Theory to the problems posed for empiricism by the discussion of D2 in 187201? The fundamental problem for empiricism, as we saw, is the problem how to getfrom sensation to content: the problem of how we could start with bare sense-data, and build up out of them anything that deserved to be calledmeaning. Plato thinks that there is a good answer to this, though it is not an empiricist answer. Sense experience becomes contentful when it is understood and arranged according to the structures that the Forms give it. So to understand sense experience is, in the truest sense, to give an account for it.The empiricist cannot offer this answer to the problem of how to get from sensation to content without ceasing to be an empiricist. What the empiricistcando is propose that content arises out of sets of sense experiences. We get to the level of belief and knowledge only when we start to consider such sets: before that we are at the level only of perception. Our beliefs, couched in expressions that refer to and quantify over such sets, will then become knowledge (a) when they are true, and (b) when we understand the full story of their composition out of such sets.If this is the point of the Dream Theory, then the best answer to the question Whose is the Dream Theory? is It belongs to the empiricist whom Plato is attacking.8.2 Critique of the Dream Theory: 202d8206c2The Dream Theory says that knowledge ofOis true belief aboutOplus an account ofO's composition. IfOis not composite,Ocannot be known, but only perceived (202b6).Socrates' main strategy in 202d8206c2 is to attack the Dream's claim that complexes and elements are distinguishable in respect of knowability. To this end he deploys a dilemma. A complex, say a syllable, is either (a) no more than its elements (its letters), or (b) something over and above those elements.202d8203e1 shows that unacceptable consequences follow from alternative (a), that a complex is no more than its elements. If I am to know a syllableSO, and that syllable is no more than its elements, then I cannot know the syllableSOwithout also knowing its elementsSandO. Indeed, it seems that coming to know the partsSandOis both necessary and sufficient for coming to know the syllableSO. But if that is right, and if the letter/syllable relation models the element/ complex relation, then if any complex isknowable, its elements will be knowable too; and if any complex's elements areunknowable, then the complex will be unknowable too. This result contradicts the Dream Theory.203e2205e8 shows that unacceptable consequences follow from alternative (b), that a complex is something over and above its elements. In that case, to know the syllable is to know something for which knowledge of the elements is not sufficient. The syllable turns out to be a single Idea that comes to be out of the fitted-together elements (204a1-2). But then the syllable does not have the elements as parts: if it did, that would compromise its singularity. And if the elements are not the parts of the syllable, nothing else can be. So the syllable has no parts, which